Integrated circuits are widely used in the electrical and computer industries. Typically, they are used in conjunction with other electrical components attached to electronic substrates such as printed circuit boards.
The actual integrated circuit is contained in a chip carrier with electrical contacts (leads) on the outside of the chip carrier. Chip carriers which have two parallel sets of leads are referred to as dual-in-line packages (DIPs). The increasing complexity and density of circuitry within an integrated circuit has made it common to find chip carriers having leads extending from all four sides of a substantially square package.
The chip carrier leads can be connected to a printed circuit board either directly or through an intermediary device such as a chip carrier connector or socket. Soldering the chip carrier directly on to a printed circuit board is a common practice, but is not a desirable method for all integrated circuits. Particularly sensitive chips such as processors or memory are susceptible to damage from voltage spikes or excessive heat. Both of these conditions may arise during production soldering. Also, it is often necessary or desirable to have easy replacement or substitution of chips. Once chips are soldered to a printed circuit board, it can be impractical to replace them.
One solution to the above problems is to solder a chip carrier connector or socket onto the printed circuit board and insert the chip carrier into the connector at a later time during production. This solution still has some problems, as it may be necessary to drill numerous holes in the printed circuit board to accommodate the leads of the connector. Drilling increases both the cost and the complexity of printed circuit board design and production. Additionally, in multilayer circuit board, drilling may take up valuable "real estate" on the different layers of the circuit board. Yet another problem with chip carrier connectors or sockets which have spring contacts is that these contacts introduce inductances and capacitances which limit the switching times of the circuitry. Usually, these spring contacts are long to develop the desired springiness for insertion, retention and withdrawal of the chip carrier. Besides adding to the undesirable inductances and capacitances, long spring contacts add to the height or profile of the connector.
Another problem which arises with solder connections involves the differences in the coefficients of thermal expansion between the chip carriers and the electronic substrates. As different parts expand at different rates, rigid connections (i.e. solder connections) may cause one or both of the parts to break. Having identical coefficients of thermal expansion between electrical components is usually a very expensive and complicated engineering and manufacturing endeavor.
Elastomeric elements have been used to address some of the problems in connecting chip carriers to printed circuit boards which are described above. For example, in U.S. Pat. No. 4,652,973, issued Mar. 24, 1987 to Paul A. Baker et al. there is described an apparatus for mounting ceramic chip carrier devices onto printed circuit boards using both metal and elastomeric contact units. In the Baker apparatus, contact is made between the chip carrier and the printed circuit board from the bottom side of the chip carrier. This design requires a cover to maintain contact between the chip carrier and the elastomeric elements. U.S. Pat. No. 4,144,648, issued Mar. 20, 1972 to Steven L. Grovender, et al., describes a connector for mounting a semiconductor package to a printed circuit board. Grovender requires that holes be drilled in the circuit board to mount a frame upon which a cover is attached. The cover is necessary to apply pressure to the chip carrier to maintain contact with the elastomeric elements.
The Baker et al. and Grovender et al. patents are but two examples of chip carrier connectors using elastomeric elements in which contact between the chip carrier and the elastomeric elements is effected in the direction of insertion of the chip carrier into the connector. Besides requiring a lid to clamp the chip carrier in place, which adds cost to the assembly, the lid also adds to the height of the connector. Also, a chip carrier is vulnerable to breakage with pressure applied across its thickness. In addition, a mechanical stop should be provided in the connector recess to prevent canting of the chip carrier rather than using the elastomeric elements for this purpose. This makes the socket height sensitive which the result that accuracy in the formation of the socket is required to assure that proper contact between the chip carrier and the elastomeric elements is established.